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Which port pin requires external pull-up resistor?
An external pull-up resistor is needed when Port 0 is defined as an output port. Port 0 of the 8051 has two main functions: To be used as a simple input-output port and to access external memory in conjunction with Port 2.
What is the purpose of a pull-up resistor connected to a microcontroller input?
Pull-up resistors are used to solve the dilemma for the microcontroller by pulling the value to a logical high state, as seen in the follow figure. Without the pull-up resistor, the MCU’s input would be floating when the switch is open and pulled down to a logical low only when the switch is closed.
Why do Port 0 pins need external pull-up resistors?
In same way we have open drain o/p in 8051 port0. The output essentially acts as either an open circuit (no connection to anything) or a connected to ground. we use external pullup resistor to provide high volt (1) rather than providing open circuit output.
What is the purpose of pullup resistors?
In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC.
Why do microcontrollers use pull up and pull down resistors?
As you stated, using pullup/pulldown resistors on pins expected to be output pins can be there to guarantee an input state. This is done to mitigate firmware/MCU failure, but will only work to protect against Hi-impedance state (basically the pin is configured as input by accident).
What happens to the pins in a microcontroller?
These pins are usually tied to internal pull-up or pull-down resistors; leaving them floating usually does not affect the algorithm of the microcontroller. However, keeping the input pins floating makes them a perfect magnet for attracting electrostatic discharges (ESD) or electromagnetic interference (EMI).
How does a pull up resistor work in Arduino?
With a pull-up resistor, the input pin will read a high state when the button is not pressed. In other words, a small amount of current is flowing between VCC and the input pin (not to ground), thus the input pin reads close to VCC. When the button is pressed, it connects the input pin directly to ground.
What should the impedance of a pull up resistor be?
The general rule for condition 2 is to use a pull-up resistor (R1) that is an order of magnitude (1/10th) less than the input impedance (R2) of the input pin. An input pin on a microcontroller has an impedance that can vary from 100k-1MΩ.